Hydraulic press



Feb. 13, 1940.

R. w. DINZL 2,189,858

HYDRAULIC PRESS Filed Nov. 9, 1955 INVENTOR E. MD/nz/ Patented Feb. 13, 1940 UNITED STATES PATENT OFFICE HYDRAULIC PRESS tion of Delaware Application November 9, 1935, Serial No. 49,049

10 Claim.

This invention relates generally to hydraulic presses and more particularly to an improved control system for minimizing pressure shocks in the operating fluid.

a It is customary to operate hydraulic presses with reversible pumps arranged so that the pressing stroke is performed by forward operation of the pump and the return stroke is performed by reverse operation of the pump. Difliculty has "iii sometimes been experienced due to pressure shocks in the operating fluid at the moment when the pump reverses to return the press. Various arrangements have heretofore been proposed to overcome this difliculty, but such prior devices it are deficient in various respects.

It is one object of my invention to provide an improved control system adapted to effectively minimize the possibility of pressure shocks or surges being created. A further object is to pro- 39 vide an improved control system that is operative to cure the cause of pressure surges thereby effectively eliminating the same. A more specific object is to accomplish this improved control in a manner that is simple, economical and positive in operation. In one specific aspect of the invention I accomplish this by providing a control system that positively prevents reversal of a pump until pressure conditions in the fluid system have acquired a predetermined condition whereby reversal of the pump will not create any serious pressure shocks, the reversal of the pump being initially determined by the platen reaching its lower position whereupon either a position or pressure reversing control is ren- 35 'dered operative.

Other objects and advantages will be more apparent-to those skilled in the art from the following description of the accompanying drawing in which the figure is a diagrammatic out- 40 line of my improved control system applied to a press.

In the particular embodiment of the invention which is disclosed herein merely for the purpose of i lustrating one specific form among 45 possible others that the invention might take in practice, I have diagrammatically shown a press having a lower stationary platen l and an upper platen or die slide 2 actuated by a main ram 3 and cylinder 5. A filling valve 5, normally urged to its closed position by a light spring, is adapted to permit fluid under low pressure to flow freely into the cylinder 4 from a filling tank 6 during initial down movement of the ram. A pilot piston and cylinder generally 55 indicated at l is adapted to be supplied with f to fill the cylinder. When a work piece resists pressure for opening filling valve to permit free return of fluid from main cylinder 4 to the filling tank when the ram 3 is moved upwardly by draw-back rams and cylinders 8. The foregoing is merely a disclosure of ele- 5 mental parts of a press which in actual practice may have various forms and multiplicity of slides or operating controls for effecting any desired functions. In any of these cases, the principles of my improved control system may be employed as will be apparent from the following disclosure.

Preferably a power driven reversible pump 9 is used of any suitable variable positive displacement .type such as is well known in the art, together with well-known mechanism diagrammatically indicated at it for effecting forward or reverse operation of the pump. The combination of control elements and their structure will be more readily understood by a joint description thereof with the mode of operation. To start the press down for the pressing operation, a hand lever H is moved to its down position and held by a latch l2 thereby shifting a control rod I3 and pump control Hi so as to adjust the pump for forward operation. The pump thereupon draws fiuid from draw-back cylinder 8 through a pipe 84, now functioning as the pump suction, and discharges fluid through a pipe IE to main cylinder 4. The exhaust of fluid from draw-back cylinders 8 permits ram 3 and platen 2 to fall by gravity during which. time liquid in filling tank 6 opens filling valve 5 to permit a large volume of low pressure liquid movement of platen 2 or the platen is otherwise slowed down, then pump pressure builds up in cylinder 4 to effect the final pressing action. When the pump pressure begins to increase it is transmitted through a pipe l6 and upon reaching a predetermined value raises a plunger I1 which is normally biased downwardly by an adjustable spring or other equivalent means. When plunger I1 is raised, it releaseslatch l2 whereupon a spring l8 rotates hand lever H in a counterclockwise direction and simultaneously moves pump control rod l3 downwardly to adjust the pump stroke toward its neutral position.

Simultaneously with release of latch H by pressure operation of plunger H, the predetermined main cylinder pressure is transmitted through a pipe l9 to raise what might be termed a neutral control plunger 20 whose stem is raised so as to form a stop for preventing counterclock- 55 This operation avoids any wise movement of hand lever ll past its horizontal neutral position. Hence, when the predetermined main cylinder pressure is reached for effecting press reversal, rod l3 and control I can only adjust pump 9 to its neutral position.

Before permitting the pump to pass into its reversing position so as to move the platen and main ram upwardly, I insure that pressure in main cylinder 4 is first reduced to permit opening of filling valve in a manner to be described shortly. After the filling valve opens, then the pump is moved to its reversing position so as to supply fluid to draw-back cylinders 8.

possibility of supplying reversing fluid to the draw-back cylinders while return movement of the ram is resisted by pressure fluid locked in the main cylinder under a closed filling valve. If the pump were reversed before the main ram and platen were able to freely move upwardly instantly, then the pump would create. a serious pressure shock. To accomplish my improved operation, I provide an auxiliary pump 22 driven in any suitable manner but preferably from the same motor which drives main pump 9. The auxiliary pump supplies fluid from a sump 23, through a pipe 24 to a three-way valve 25 and thence through a pipe 26 to move a plunger 21 for opening a check valve 28. Fluid from main cylinder 4 then flows through a pipe 29, a valve 28 and a suitable adjustable pressure reducing orifice 30 to filling tank 6. It will be understood that valve 25 was moved downwardly when hand lever II was unlatched and moved to its horizontal neutral position by spring l8, valve 25 prior to this operation being in a raised position whereby fluid from auxiliary pump 22 was bypassed back to sump 23 through a pipe 3| while at the same time pilot cylinder 1 and the cylinder of piston 21 are connected to exhaust through pipe 26, port 26a and an exhaust outlet 3la. When pressure in main cylinder 4 is sufiiciently reduced by discharge of main cylinder fluid throughpipes 29 and orifice 30 into filling tank 6, then filling valve 5 will be readily opened by pressure supplied to pilot cylinder 1 through pipes 24 and -32. Also upon reduction of pressure in main cylinder 4, plunger will drop so as to permit spring I8 to move pump control rod l3 downwardly for shifting main pump 9 to its reversing position, whereupon fluid is discharged through pipe l4 to draw-back cylinders 8 for returning the press to its upper position. During the same time a portion of the fluid in main cylinder 4 is drawn through pipe 15 to pump 9. When valve and rod l3 move to their full down or reversing position, auxiliary fluid pressure is still supplied to pilot cylinder I and plunger 21 through ports 24a, 26a and pipe 26. When the press reaches its upper position, the pump is returned to neutral by manual movement of hand lever II to its horizontal position. Check valve 28 is closed during the pressing operation. From the foregoing disclosure it is seen that before the main pump can be thrown into its reversing position, the pressure in main cylinder 4 is sufliciently reduced to permit opening of filling valve 5 whereupon when the pump is thrown into reversing position only suflicient draw-back pressure will be required to raise the dead-weight of ram 3 and platen 2 without any possibility of the return movement being resisted by pressure looked in main cylinder 4. If-

the pump should be thrown to its reverse position before the pressure in main cylin er 4 is reduced, or before the filling valve 5 has had an opportunity to open, then it is seen that an excessive draw-back pressure would be created in case the pump were suddenly reversed thus causing a pressure shock or surge in the system with consequent wear and tear on the pump and unnecessary strains on the press structure and control apparatus. However I have provided a relatively simple and yet positive control for preventing or minimizing pressure shocks during reversal of the press.

It will of course be understood that various changes in details of construction and arrangement of parts may be made by those skilled in the art without departing from the spirit of the invention as set forth in the appended claims.

I claim:

1. In combination, a hydraulic press having a main ram and cylinder and a pull-back ram and cylinder, reversible pumping means for alternatively supplying fluid pressure to said cylinders to effect pressing and pull-back strokes of said ram, means for initiating reversal of said pumping means to effect a pull-back stroke automatically upon occurrence of a predetermined condition of operation of said main ram during a pressing stroke, means whereby pressure in said main cylinder can be reduced prior to reversal of said pumping means, and means operable independently of said initiating means for controlling the same so as to inhibit reversal of said pumping means automatically until the pressure in the main cylinder is reduced to a predetermined value whereupon said initiating means effects reversal of said pumping means.

2. In combination, a hydraulic press having a main cylinder and ram and a draw-back cylinder and ram, a filling tank having a filling valve adapted to permit free flow of fluid between said filling tank and main cylinder during movement of the main ram in opposite directions, a reversible pump for supplying fluid pressure alternatively to said cylinders, means for moving said pump from its forward pressing position to neutral and thence to its reversing position, means for restraining reversing movement of the pump after it is moved to its neutral position from its forward preming position but adapted to allow the pump to be moved to its reverse position by 'said moving means automatically upon occurrence of a drop of pressure in the main cylinder brought about substantially by the opening of said filling valve, means for allowing the pressure in the main cylinder to drop to a predetermined value automatically after said pump is moved to its neutral position, and means whereby said filling valve is adapted to open automatically upon occurrence of said predetermined drop of pressure in the main cylinder whereby the opening of said filling valve causes the main cylinder pressure to drop thereby rendering said restraining means for the pump effective in allowing the pump to be moved to its reversing position and supply fluid to the draw-back cylinders without the presence of substantial resistment of the ram therein, a reversible pump for supplying fluid pressure alternatively to said main and pull-back cylinders, and means for supplying fluid pressure to said pilot cylinder thereby to effect an opening force on the filling valve prior to the supply ,of fluid to said drawback cylinder, means for reducing pressure in vthe main cylinder substantially when the fluid pressure is supplied to said pilot cylinder whereby when the main cylinder pressure drops to a predetermined value the filling valve can open, and means for reversing said pump to effect a pull-back operation after said predetermined drop of main cylinder pressure.

4. In combination, a hydraulic press having a main cylinder and ram and a draw-back cylinder and ram, a source of fluid pressure for operating said rams, means including a lever for initiating supply of fluid to the main cylinder, means for latching said lever in its pressing position, means responsive to pressure in said main cylinder for releasing said latch automatically when a predetermined pressure is reached in said main cylinder, means for shifting said lever 'when said latch is released so as to discontinue supply of fluid to said main cylinder, and means for holding said lever in neutral position so as to automatically prevent supply of fluid to said draw-back cylinder until said main cylinder pressure is reduced to a predetermined value whereupon said lever is allowed to move from its neutral position to its reversing position to supply fluid to the draw-back cylinders.

5. In combination, a hydraulic press having a main cylinder and ram and a draw-back cylinder and ram, a reversible positive displacement pump, means for supplying fluid from said pump to said main cylinder to eflfect a pressing operation, means for reversing said pump to supply fluid to the draw-back cylinders, fluid pressurecontrolled means responsive to a predetermined increase of pressure in said main cylinder for initiating reversal of said pump, and means separate from said initiating means and being controlled by a reduction in pressure in said main cylinder for automatically inhibiting said pump reversal until occurrence of a predetermined reduction of pressure in said main cylinder.

6. In combination, a hydraulic press having a main cylinder and ram and a draw-back cylinder and ram, a reversible positive displacement neutral position.

pump, means for shifting said pump in a forward direction for supplying fluid to said main cylinder for effecting the pressing operation. means for shifting said pump from its forward position through neutral to its reverse position, 5 means for rendering said shifting means effective to move the pump from its forward position to neutral automatically upon occurrence of a predetermined pressure in said main cylinder, and means responsive to pressure in said main cylinder for inhibiitng shifting of said pump from its neutral position to its reversing position until the main cylinder pressure is reduced to a predetermined value. 1

7. The combination set forth in claim 6 further characterized by the provision of means for effecting release of pressure in said main cylinder automatically when said pump is shifted to substantially its neutral position prior to the reversing operation thereby to insure minimum resistance to draw-back movement of the main ram.

8. The combination set forth in claim 6 further characterized by the provision of a passage having an orifice for controlling discharge of fluid from said main cylinder to effect said reduction of pressure therein.

9. The combination set forth in claim 6 further characterized by the provision of a passage having an orifice for controlling discharge of fluid from said main cylinder to eilect said re-' duction of pressure therein, a normally closed valve in said passage, and means for effecting opening of said valve automatically when said pump is shifted from its forward position substantially to its. neutral position.

10. The combination set forth in claim 6 further characterized by the provision of a passage having an oriflce for controlling discharge 0! fluid from said main cylinder to efiect said reductlon of pressure therein, a normally closed valve in said passage to prevent discharge of main cylinder fluid through said orifice, fluid pressure controlled opening means for said valve and a continuously operating auxiliary pump, and means for supplying fluid from, said auxillaw pump to said valve opening means automatically when the reversible pump is shifted to its RICHARD W. DINZL. o 

